The present invention relates to a thermoplastic resin composition which excels especially in impact resistance, dimension stability and rigidity, and also excels in appearance, fluidity and paint film adhesion property, and further which is widely used for various technical fields such as electric machines, electronics and automobile. Especially, the thermoplastic resin composition is extremely useful as manufacturing materials for exterior parts of automobile.
Since polyamide resins are excellent in mechanical properties such as moldability, chemical resistance, tensile strength and bending strength, and also abrasion resistance, polyamide resins are widely used in various technical fields such as electric machine parts, electronics parts, machine parts and automobile parts. However, there is a problem of poor dimension stability (linear expansion coefficient) in obtained molded products. For example, in case where a molded product obtained from a polyamide resin composition is used with a metallic part in combination, there are problems of dimension difference therebetween and engagement trouble therebetween when using under high temperature circumstance, because the linear expansion coefficient of the resin molded part is larger than that of metallic parts.
Further, in case where paint is applied on a surface of plastic molded product and this plastic molded product is used under high temperature circumstance, the formed paint film on the surface of molded product is peeled off or fine cracks are formed on the paint film surface so that there arise problems of deterioration of appearance and design thereof, because of difference of expansion coefficient between the paint and plastic molded product.
On the other hand, it has been progressed to use plastic materials for exterior automobile parts such as fenders, door panels, bonnets and roof panels, which are generally formed with metallic materials in view of enabling lightening, design variety and module assembling. In these applications, there are required materials having high level quality of impact resistance, dimension stability (linear expansion coefficient), rigidity, fluidity, appearance, etc.
As a method for improving the dimension stability and rigidity of polyamide resin, there has been known a method in which an inorganic filler is blended into a polyamide resin. However, in this method, there is a problem that the application field is limited because the impact resistance is remarkably deteriorated and also the appearance is deteriorated.
As an improvement strategy of the above problem, for example, in order to improve the impact resistance of polyamide resin, it is widely used to add a rubber polymer thereinto. Further, in order to enhance the compatibility between the polyamide resin and rubber polymer, it is known as a conventional manner to modify the rubber polymer with an unsaturated carboxylic acid or derivative thereof.
For example, as the above polyamide resin composition, there is disclosed a composition comprising polyamide resin and modified hydrogenated block copolymer and also described that an inorganic filler can be blended as an optional component thereinto (refer to Patent Document 1). Further, there is disclosed a polyamide resin composition which comprises a polyamide resin, an inorganic filler, modified styrene-olefin based copolymer and has excellent metal plating property and paint film adhesion property (refer to Patent Document 2). However, in the above conventional techniques, the balance of impact resistance, dimension stability and rigidity is insufficient. To this matter, for example, in order to improve the impact resistance, the blending content of rubber polymer is increased. However, since the dimension stability and rigidity are remarkably deteriorated by increasing blending content of rubber polymer, it is necessary to improve the balance of impact resistance, dimension stability and rigidity.
Still further, there is disclosed a polyamide resin composition which comprises (A) polyamide resin, (B) hydrogenated block copolymer comprising-block “a” of vinyl aromatic compound polymer and block “b” of olefin compound polymer and (C) modified block copolymer obtained by addition of carboxylic acid or derivative group thereof to the above hydrogenated block copolymer, has an excellent impact resistance and a good property balance of elasticity, heat resistance and weld portion strength, and is improved in moldability and appearance of molded product (refer to Patent document 3). Also, there is disclosed a polyamide resin composition which comprises (A) polyamide resin having specific end groups, (B) hydrogenated block copolymer comprising a vinyl aromatic compound and conjugated diene compound, (C) modified block copolymer obtained by bonding carboxylic acid group or derivative group thereof to a hydrogenated block copolymer comprising a vinyl aromatic compound and conjugated diene compound, (D) ethylene-α-olefin based copolymer and (E) olefin based polymer having acid anhydride group at the only chain end, and is improved in low temperature impact resistance (refer to Patent document 4). In this reference, there is a further description that an inorganic filler can be added as an optional component into these compositions.
However, in these inventions, there is an only disclosure of blending effect of the inorganic filler within the combination of the above specific components and no concrete embodiment of blending the inorganic filler in Examples. Therefore, there is no description nor suggestion that it is necessary to blend a specific inorganic filler in order to obtain a polyamide resin composition having an extremely good balance of impact resistance, dimension stability and rigidity.
Further, there is disclosed an impact resistance polyamide resin composition comprising a polyamide resin, a functioned (acid modified) triblock copolymer, an unfunctioned ethylene-propylene copolymer and a fibrous filler (refer to Patent document 5). However, in this invention, there is a problem of deterioration of appearance of obtained molded product caused by using the fibrous filler. Further, in this reference, there is no teaching that it is necessary to blend a specific inorganic filler thereinto in order to attain good appearance while maintaining the high level balance of impact resistance, dimension stability and rigidity. Therefore, there is a strong demand to provide a thermoplastic resin composition having excellent balance of impact resistance, dimension stability and rigidity as well as good appearance.
Still further, in Patent document 6, there is disclosed a composition comprising (A) polyamide resin, (B) copolymer of olefin based compound and compound having an unsaturated group and together with polar group typically such as ethylene-acrylic acid copolymer and (C) conductive material, and which composition is excellent in mechanical properties, fluidity and electrical properties such as conductivity.
To the said composition, the present inventor has further studied to obtain a molding product having good appearance by preventing from a problem that not good marks formed at releasing remain to the surface of molding product by improvement of releasability when molding.    Patent document 1: Japanese Patent Publication (KOKOKU) No. 63-44784    Patent document 2: Japanese Patent Publication (KOKOKU) No. 8-11782    Patent document 3: Japanese Patent Publication (KOKOKU) No. 7-26019    Patent document 4: Japanese Patent No. 3330398    Patent document 5: Japanese Patent Publication (KOKOKU) 7-49522    Patent document 6: Japanese Patent Application Laid-Open (KOKAI) No. 2003-64254